Abstract

An experimental set-up was used to visually observe the characteristics of bubbles as they moved up a column holding xanthan
gum crystal suspensions. The bubble rise characteristics in xanthan gum solutions with crystal suspension are presented
in this paper. The suspensions were made by using different concentrations of xanthan gum solutions with 0.23 mm mean
diameter polystyrene crystal particles. The influence of the dimensionless quantities; namely the Reynolds number, Re, the
Weber number, We, and the drag co-efficient, cd, are identified for the determination of the bubble rise velocity. The effect of
these dimensionless groups together with the Eötvös number, Eo, the Froude number, Fr, and the bubble deformation parameter,
D, on the bubble rise velocity and bubble trajectory are analysed. The experimental results show that the average bubble
velocity increases with the increase in bubble volume for xanthan gum crystal suspensions. At high We, Eo and Re, bubbles
are spherical-capped and their velocities are found to be very high. At low We and Eo, the surface tension force is significant
compared to the inertia force. The viscous forces were shown to have no substantial effect on the bubble rise velocity
for 45 < Re < 299. The results show that the drag co-efficient decreases with the increase in bubble velocity and Re. The trajectory
analysis showed that small bubbles followed a zigzag motion while larger bubbles followed a spiral motion. The
smaller bubbles experienced less horizontal motion in crystal suspended xanthan gum solutions while larger bubbles exhibited
a greater degree of spiral motion than those seen in the previous studies on the bubble rise in xanthan gum solutions
without crystal.

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